Theaflavin -3,3'-digallate/ethanol: a novel cross-linker for stabilizing dentin collagen

Objectives

To study the ability of theaflavin-3,3'-digallate (TF3)/ethanol solution to crosslink demineralized dentin collagen, resist collagenase digestion, and explore the potential mechanism.

Methods

Fully demineralized dentin blocks were prepared using human third molars that were caries-free. Then, these blocks were randomly allocated into 14 separate groups (n = 6), namely, control, ethanol, 5% glutaraldehyde (GA), 12.5, 25, 50, and 100 mg/ml TF3/ethanol solution groups. Each group was further divided into two subgroups based on crosslinking time: 30 and 60 s. The efficacy and mechanism of TF3's interaction with dentin type I collagen were predicted through molecular docking. The cross-linking, anti-enzymatic degradation, and biomechanical properties were studied by weight loss, hydroxyproline release, scanning/transmission electron microscopy (SEM/TEM), in situ zymography, surface hardness, thermogravimetric analysis, and swelling ratio. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were utilized to explore its mechanisms. Statistical analysis was performed using one and two-way analysis of variance and Tukey's test.

Results

TF3/ethanol solution could effectively crosslink demineralized dentin collagen and improve its resistance to collagenase digestion and biomechanical properties (p < 0.05), showing concentration and time dependence. The effect of 25 and 50 mg/ml TF3/ethanol solution was similar to that of 5% GA, whereas the 100 mg/mL TF3/ethanol solution exhibited better performance (p < 0.05). TF3 and dentin type I collagen are mainly cross-linked by hydrogen bonds, and there may be covalent and hydrophobic interactions.

Conclusion

TF3 has the capability to efficiently cross-link demineralized dentin collagen, enhancing its resistance to collagenase enzymatic hydrolysis and biomechanical properties within clinically acceptable timeframes (30 s/60 s). Additionally, it exhibits promise in enhancing the longevity of dentin adhesion.

Applications of scanning electron microscopy and focused ion beam milling in dental research

The abilities of scanning electron microscopy (SEM) and focused ion beam (FIB) milling for obtaining high-resolution images from top surfaces, cross-sectional surfaces, and even in three dimensions, are becoming increasingly important for imaging and analyzing tooth structures such as enamel and dentin. FIB was originally developed for material research in the semiconductor industry. However, use of SEM/FIB has been growing recently in dental research due to the versatility of dual platform instruments that can be used as a milling device to obtain low-artifact cross-sections of samples combined with high-resolution images. The advent of the SEM/FIB system and accessories may offer access to previously inaccessible length scales for characterizing tooth structures for dental research, opening exciting opportunities to address many central questions in dental research. New discoveries and fundamental breakthroughs in understanding are likely to follow. This review covers the applications, key findings, and future direction of SEM/FIB in dental research in morphology imaging, specimen preparation for transmission electron microscopy (TEM) analysis, and three-dimensional volume imaging using SEM/FIB tomography.

Effect of an extrafibrillar dentin demineralization strategy on the durability of the resin-dentin bond

OBJECTIVES

This study aimed to evaluate the potential of the extrafibrillar dentin demineralization strategy on the long-term dentin bond strength of an etch-and-rinse adhesive.

METHODS

A water-soluble glycol chitosan-EDTA (GCE), a chelating conditioner, was synthesized and subjected to size-exclusion dialysis to obtain molecules >40 kDa. The conjugation of EDTA to glycol chitosan was analyzed by Fourier transform infrared (FTIR) spectroscopy. Mid-coronal dentin surfaces of 80 teeth were either acid-etched with 35% phosphoric acid or conditioned with 25 mg/mL GCE (n = 40) and thoroughly water-sprayed before applying the etch-and-rinse adhesive Adper Single Bond Plus and placing Z250 composite resin (3 M Oral Care; St Paul, MN, USA). Resin-bonded specimens were prepared into beams with a cross-sectional area of about 0.9 mm² vertically through the resin-dentin interfaces before the microtensile bond strengths (MTBS) were determined immediately or after 3, 6, or 12 months of water storage. The resin-dentin interfaces were analyzed using transmission electron microscopy (TEM). The MTBS data were analyzed using two-way ANOVA followed by the LSD post-hoc multiple comparisons (P < 0.05).

RESULTS

FTIR spectra showed that EDTA was successfully conjugated to glycol chitosan. The phosphoric acid-etching group and GCE-conditioning group showed similar bond strength values after 24 h of water storage. The bond strength of the phosphoric acid-etching group after 12-month water aging was significantly reduced from 51.61 ± 3.30 MPa to 38.57 ± 4.81 MPa, while the bond strength of the GCE-conditioning group was not significantly reduced from 50.28 ± 3.62 MPa to 46.40 ± 4.71 MPa.The degradation of the hybrid layer could be detected in the phosphoric acid-etching group after 12 months of water aging, but not in the GCE-conditioning group.

CONCLUSION

The extrafibrillar dentin demineralization strategy using GCE conditioner could defy the hybrid layer degradation of the dentin bond after 12 months of water aging and enhance the dentin bond durability of the etch-and-rinse adhesive Adper Single Bond Plus.

Reconstruction of a Demineralized Dentin Matrix via Rapid Deposition of CaF2 Nanoparticles In Situ Promotes Dentin Bonding

Dentin bonding based on a wet-bonding technique is the fundamental technique used daily in clinics for tooth-restoration fixation and clinical treatment of tooth-related diseases. Limited bonding durability led by insufficient adhesive infiltration in the demineralized dentin (DD) matrix is the biggest concern in contemporary adhesive dentistry. This study proposes that the highly hydrated noncollagenous protein (NCP)-formed interfacial microenvironment of the DD matrix is the root cause of this problem. Meanwhile, the endogenous phosphate groups of the NCPs are used as pseudonuclei to rapidly induce the formation of amorphous CaF₂ nanoparticles in situ in the interfacial microenvironment. The DD matrix is thus reconstructed into a novel porous structure. It markedly facilitates the infiltration of dentin adhesives in the DD matrix and also endows the DD matrix with anticollapsing capability when water evaporates. Whether using a wet-bonding or air-drying mode, the bonding effectiveness is greatly promoted, with the 12 month bonding strength being about twice that of the corresponding control groups. This suggests that the nanoreinforced DD matrix eliminates the dependence of bonding effectiveness on the moisture status of the DD surface controlled only by experiences of dentists. Consequently, this bonding strategy not only greatly improves bonding durability but also overcomes the technical sensitivity of bonding operations of the total-etched bonding pattern. This exhibits the potential to promote dentin bonding and is of great significance to dentistry.

STEM and HRTEM studies of accumulated deposits on human tooth surface

The aim of this study was to clarify the fine structure of accumulated deposits on the surface of teeth that are considered to affect the gloss of teeth. The study was carried out using, as specimens, human incisor teeth having gloss, which were extracted from teenage donors and those incapable of showing gloss even by brushing which were extracted from donors in their 50s. Thin longitudinal sections of tooth enamel with accumulated deposits on the surface were prepared by focused ion beam (FIB) milling, and the fine structure was analyzed using a scanning transmission electron microscope (STEM) and a high resolution transmission electron microscope (HRTEM). By FIB, thin longitudinal sections could be prepared from tooth enamel together with organic and inorganic substances accumulated on the surface without artifacts. The accumulated deposits on the surface of teeth having gloss were composed of organic substances. However, it was first revealed by STEM observation that the accumulated solid deposits on the surface of teeth having no gloss had a complicated structure wherein inorganic and organic substances coexisted. It is suggested that the organic substances contain proteins derived from saliva. The inorganic substances were spherical and needle-like hydroxyapatites (HAs). It is considered that amino acids constituting the proteins affected the nucleus formation and the crystal formation of HA. It is considered that the unevenness of the accumulated deposits existing on the surface of tooth enamel having no gloss causes the decrease in gloss of teeth due to diffuse reflection of light.

Nanoleakage in Hybrid Layer and Acid-Base Resistant Zone at the Adhesive/Dentin Interface

The aim of interfacial nanoleakage evaluation is to gain a better understanding of degradation of the adhesive-dentin interface. The acid-base resistant zone (ABRZ) is recognized at the bonded interface under the hybrid layer (HL) in self-etch adhesive systems after an acid-base challenge. The purpose of this study was to evaluate nanoleakage in HL and ABRZ using three self-etch adhesives; Clearfil SE Bond (SEB), Clearfil SE One (SEO), and G-Bond Plus (GBP). One of the three adhesives was applied on the ground dentin surface and light cured. The specimens were longitudinally divided into two halves. One half remained as the control group. The others were immersed in ammoniacal silver nitrate solution, followed by photo developing solution under fluorescent light. Following this, the specimens were subjected to acid-base challenges with an artificial demineralization solution (pH4.5) and sodium hypochlorite, and prepared in accordance with common procedures for transmission electron microscopy (TEM) examination. The TEM images revealed silver depositions in HL and ABRZ due to nanoleakage in all the adhesives; however, the extent of nanoleakage was material dependent. Funnel-shaped erosion beneath the ABRZ was observed only in the all-in-one adhesive systems; SEO and GBP, but not in the two-step self-etch adhesive system; SEB.

Marginal Leakage of Class V Composite Restorations Assessed Using Microcomputed Tomography and Scanning Electron Microscope

Objective

The aim of the study was to compare in Class V composite restorations marginal leakage measurements obtained with microcomputed tomography (micro-CT) and scanning electron microscopy (SEM) observations.

Methods

Class V cavities were prepared on 10 human molars and restored using Optibond FL (Kerr, Orange, CA, USA) and Premise Flowable (Kerr). Sealing ability was evaluated by assessing silver-nitrate penetration depth along enamel and dentin margins. Leakage was quantified using a scoring system. Micro-CT analysis provided 502 cross-sectional images for each tooth. Microleakage evaluation was performed first on three cross-sections corresponding to the sections examined by SEM, then on all 502 of the obtained micro-CT images. SEM observations were performed first at 20× magnification, then, if showing a zero score, at 80× magnification. Enamel and dentin microleakage scores assigned to corresponding sections through micro-CT and SEM (20×) were compared (Wilcoxon signed-rank test, α=0.05).

Results

No statistically significant difference in leakage scores emerged between micro-CT and 20×-magnification SEM. Eight tooth sections that were given a zero score under SEM at 20× magnification showed to be infiltrated at the higher magnification (80×). For five teeth a higher score was assigned following scanning of 502 cross-sections than based on the observation of three sections.

Conclusions

Micro-CT presents as a valid, nondestructive in vitro method to quantitatively evaluate marginal leakage of adhesive restorations.

Exploiting the potential of free software to evaluate root canal biomechanical preparation outcomes through micro-CT images

AIM

To propose an automated image processing routine based on free software to quantify root canal preparation outcomes in pairs of sound and instrumented roots after micro-CT scanning procedures.

METHODOLOGY

Seven mesial roots of human mandibular molars with different canal configuration systems were studied: (i) Vertucci's type 1, (ii) Vertucci's type 2, (iii) two individual canals, (iv) Vertucci's type 6, canals (v) with and (vi) without debris, and (vii) canal with visible pulp calcification. All teeth were instrumented with the BioRaCe system and scanned in a Skyscan 1173 micro-CT before and after canal preparation. After reconstruction, the instrumented stack of images (IS) was registered against the preoperative sound stack of images (SS). Image processing included contrast equalization and noise filtering. Sound canal volumes were obtained by a minimum threshold. For the IS, a fixed conservative threshold was chosen as the best compromise between instrumented canal and dentine whilst avoiding debris, resulting in instrumented canal plus empty spaces. Arithmetic and logical operations between sound and instrumented stacks were used to identify debris. Noninstrumented dentine was calculated using a minimum threshold in the IS and subtracting from the SS and total debris. Removed dentine volume was obtained by subtracting SS from IS.

RESULTS

Quantitative data on total debris present in the root canal space after instrumentation, noninstrumented areas and removed dentine volume were obtained for each test case, as well as three-dimensional volume renderings.

CONCLUSION

After standardization of acquisition, reconstruction and image processing micro-CT images, a quantitative approach for calculation of root canal biomechanical outcomes was achieved using free software.

The dentin organic matrix - limitations of restorative dentistry hidden on the nanometer scale

The prevention and treatment of dental caries are major challenges occurring in dentistry. The foundations for modern management of this dental disease, estimated to affect 90% of adults in Western countries, rest upon the dependence of ultrafine interactions between synthetic polymeric biomaterials and nanostructured supramolecular assemblies that compose the tooth organic substrate. Research has shown, however, that this interaction imposes less than desirable long-term prospects for current resin-based dental restorations. Here we review progress in the identification of the nanostructural organization of the organic matrix of dentin, the largest component of the tooth structure, and highlight aspects relevant to understating the interaction of restorative biomaterials with the dentin substrate. We offer novel insights into the influence of the hierarchically assembled supramolecular structure of dentin collagen fibrils and their structural dependence on water molecules. Secondly, we review recent evidence for the participation of proteoglycans in composing the dentin organic network. Finally, we discuss the relation of these complexly assembled nanostructures with the protease degradative processes driving the low durability of current resin-based dental restorations. We argue in favour of the structural limitations that these complexly organized and inherently hydrated organic structures may impose on the clinical prospects of current hydrophobic and hydrolyzable dental polymers that establish ultrafine contact with the tooth substrate.